There is an urgent need to establish noninvasive biomarkers which enable early detection of a range of diseases such as cancers and neurodegenerative disorders. Recent advances in the field of “omics” have facilitated identification of novel biomarkers from various biospecimens. This is well reflected in the recent global biomarkers market research anticipating growth from $29.3 billion in 2013 to $53.6 billion in 2018, a CAGR of 12.8% (by PRNewswire).
Recent studies have demonstrated that the tear fluid is a unique biospecimen containing mucins, lipids, more than 500 proteins, peptides, cytokines and neurotransmitters. In particular, the scarcity of albumin and immunoglobulins in tears while abundant in serum makes analysis straightforward. Changes in composition of tears have been reported in various conditions including not only local eye diseases but systemic conditions such as cancers and diabetes. The dynamic changes in composition of tears in response to systemic pathophysiologic conditions render tears as an alternative source of biomarkers.
The tear film is a kind of hydrated mucin gel containing fluid, electrolytes, proteins and other aqueous components secreted by lacrimal glands and ocular surface epitheoium, and it is covered by a lipid layer generated by meibomian glands. Tear fluids have been used to assess stress levels in individuals, specific markers such as serotonin, cortisol and DHEA levels are indicative of stress levels. Various techniques such as Gas chromatography-mass spectrometry (GC-MS), Liquid chromatography-mass spectrometry (LC-MS), Immunoassays for steroid hormones have been used to measure levels of specific markers.